Electrical radiant heater for heating heating surfaces

Abstract

An electric radiant heater (11) for heating a glass ceramic cooking surface (12) contains a dish-shaped insulator (14), to whose inner bottom surface (18) are fixed heater coils (20). The heater coils have an oval cross-section and are pressed by their narrow sides into surface (18) and fixed. The fixing pressing in takes place during the moulding of the moist insulator (14), made from fibrous material and by means of a male mould receiving the heater coils in slots.

What is claimed is: 
     
       1. Electric radiant heater for heating heating surfaces, comprising an insulator made from electrically and thermally insulating material, at least one heater coil having numerous spaced turns of electrical resistance wire being partly embedded in a surface of said insulator, the heater coil having a substantially oval coil cross-section having a cross-sectional major and a minor axis and with two facing sides each having a respective cross-sectional major and minor curvature, a portion of the heater coil being embedded at the heater coil side of major curvature whereby major axis of the coil cross-section is directed away from said surface of the insulator. 
     
     
       2. Radiant heat according to claim 1, wherein the oval coil cross-section comprises two, substantially semicircular sides, which are more curved in the apex region and sides connecting the same having a substantially linear configuration of the resistance wire. 
     
     
       3. Radiant heat according to claim 2, wherein on the outsides of the heater coil the embedding extends up to sides with a substantially linear configuration of the resistance wire. 
     
     
       4. Radiant heater according to claim 1, wherein the heater coil embedded over the entire length thereof in a substantially uniform manner for each turn, but only over a portion taking up a fraction of the turn circumference. 
     
     
       5. Radiant heater according to claim 1, wherein the insulator preponderantly comprises fibres combined into a relatively rigid body. 
     
     
       6. Radiant heater according to claim 5, wherein in the embedded portion, fibres of insulator passing into the coil interior overlap the resistance wire, but the remainder of the coil interior is substantially free from insulating material. 
     
     
       7. Radiant heater according to claim 1, wherein the embedded portion is located in depressions running along the length at the wire and which are partly open towards the surface of insulator. 
     
     
       8. Radiant heater according to claim 1, wherein the turns of resistance wire are further surrounded by the material of insulator on the outsides thereof than in the coil interior. 
     
     
       9. Radiant heater according to claim 1, wherein several different heater coils are embedded in spiral paths in an insulator. 
     
     
       10. Radiant heater according to claim 1, wherein the ratio of the major to minor axis of the oval coil cross-section is larger than 1.5 and preferably approximately 2. 
     
     
       11. Radiant heater according to claim 1, wherein the ratio of the coil pitch (h) to the diameter (d) of the resistance wire is greater than 2 and preferably between 4 and 8. 
     
     
       12. Radiant heater according to claim 1, wherein the heater coil is a press-formed coil having two lateral sides being flattened by pressing it into oval shape from circular cross-sectional shape. 
     
     
       13. Radiant heater according to claim 1, wherein the insulator is press-shaped. 
     
     
       14. Radiant heater according to claim 13, wherein the insulator is a hardened insulator. 
     
     
       15. Radiant heater according to claim 1, in which a a side of the heater coil of minor curvature provides lateral guiding means for insertion of the coils into the insulator.